1. Field of the Invention
The present invention relates to a method for producing a spacer and a spacer, which is adapted to be positioned between a pair of substrates on an electric or electronic device and to maintain a gap between such substrates.
2. Related Background Art
Recently, there is being developed a flat panel display in which electron-emitting elements of surface conduction type are arranged in a matrix array on a substrate and emitted electrons irradiate a phosphor material provided on another opposed substrate, so positioned as to hermetically seal the electron-emitting elements, thereby forming an image.
For producing a spacer for supporting substrates of such an electron beam apparatus in which an electron beam source is hermetically sealed between a pair of substrates, there is known a heat drawing method in which a base glass material of a rectangular cross section is advanced by a rotation of feed rollers so positioned as to pinch the base glass, while the advanced base glass is pinched between pull rollers and is pulled with a pull speed higher than a feeding speed of the feed rollers, and the base glass is softened by heating between the feed rollers and the pull rollers to achieve a drawing of the base glass by a speed difference between the feeding speed of the feed rollers and the pull speed of the pull rollers, thereby obtaining a drawn base glass material of a cross sectional shape similar to that of the base glass, and such drawn base glass is cut to obtain a slat-shaped spacer of a desired dimension (Japanese Patent Application Laid-open No. 2000-164129 etc.).
On the other hand, with respect to the spacer to be employed in such electron beam apparatus, there is pointed out a possibility that a part of the electrons emitted from the electron source collide with the spacer or ions formed by the emitted electrons stick to the spacer, thereby inducing a charge thereon. A charging of the spacer hinders an exact control of the trajectory of the electrons emitted from the electron source, thereby resulting in a drawback, for example, of a distortion in the displayed image.
In order to avoid such drawback, Japanese Patent Application Laid-open No. 2000-311608 discloses a technology of forming an irregular structure on the surface of the space, thereby suppressing a charging thereon. The Japanese Patent Application Laid-open No. 2000-311608 discloses, utilizing the aforementioned heat drawing method, a method of forming surface irregularities while executing the heat drawing, and a method of forming irregularities in advance on a base glass material and then heat drawing such base glass material.
In general, the drawing of a glass material is executed under heating in such a manner that the glass material has a viscosity within a range of 105 to 1010 dPa·s.
Also in the prior methods explained in the foregoing, the drawing of the glass material is executed under heating in such a manner that the glass material has a viscosity within a range of 105 to 1010 dPa·s, but in case the drawing is executed with a viscosity at a lower side, namely with a heating temperature at a higher side, both end portions of the obtained slat-shaped spacer in the longitudinal direction in the cross section tend to become rounded and expanded, as shown in FIG. 8. When the obtained slat-shaped spacer is placed on the substrate, in a position standing thereon and extending oblong along the substrate, because a contact surface of the spacer with the substrate is curved, such spacer is poor in stability and in an assembling property and is difficult to provide a sufficient supporting strength.
On the other hand, in case the drawing is executed with a viscosity at a higher side, namely with a heating temperature at a lower side, an intermediate portion of the obtained slat-shaped spacer tends to become constricted in the longitudinal direction in the cross section, as shown in FIG. 9. A spacer with such constriction cannot provide a desired strength, and, in case it is employed as a spacer positioned between a pair of substrates for example of a flat panel display, in which a space between the substrates is maintained at a reduced pressure, there may not be obtained a necessary resistance to the atmospheric pressure.
Also, in case the cross sectional shape of the spacer at the manufacture thereof is poorly controlled as explained above, the aforementioned irregularities for suppressing the charging cannot be obtained in a designed shape, whereby a desired charge suppressing effect cannot be obtained.